The present invention relates to methods and systems for the inspection of the internal walls of the tubes of fire tube boilers.
In general, two types of commercial boilers which are widely used are water tube boilers and fire tube boilers. In water tube boilers the tubes carry water and they are surrounded by combustion within the boiler. In fire tube boilers combustion occurs within the tubes and the tubes are immersed in water.
The tubes of a fire tube boiler are subjected to high heat, which fluctuates and causes stress; the build-up of decomposition products from combustion; and water leakage, should any openings develop. The tube should be inspected to determine if there is excessive build-up of decomposition products or if there is any leakage. In addition, a skilled engineer or operator may be able to determine the flame pattern and if there are problems in the combustion process, by viewing the shape, size and color of the decomposition build-up and the color of the internal tube wall.
In order to replace a leaking boiler tube it is necessary to shut-down the boiler; permit it to cool to room temperature, which may take hours; and cut-out the defective tube and weld a new tube in its place, requiring circular welds at both ends of the tube. That replacement procedure is time-consuming and costly, particularly since it must be done each time a tube develops a serious leak. Since the typical commercial boiler has many tubes, and they receive unequal stress from combustion, the tubes may start to leak in a random and unpredictable manner, requiring frequent boiler shut-downs and repairs.
An alternative to waiting for the tubes to leak before replacing them is to have the tubes inspected, for example, on a monthly schedule, by a boiler inspection service. Sucn an inspection service may utilize an oriented fiber optic bundle to visually inspect the interior wall of the tube. That type of fiber optic system is relatively costly and consequently would be utilized by an inspection service rather than by the boiler operator. In addition, the fiber optic bundle is not heat-resistant, so the boiler must be shut-down and permitted to cool, for many hours, before it may be inspected.
The analysis of the combustion process is especially important when the fuel is a slurry, for example, a coal-water or coal-oil-water slurry. When the boiler is burning a completely combustible fuel, such as natural gas or butane gas, the decomposition build-up is likely to be slow. However, if a coal slurry is incorrectly combusted, the decomposition build-up on the tube wall may be relatively rapid and its analysis may reveal if there are any combustion problems.